Department of Chemistry, Texas A&M University , College Station, Texas 77843-3255, United States.
J Phys Chem A. 2013 Dec 19;117(50):13596-604. doi: 10.1021/jp407592r. Epub 2013 Oct 17.
The infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along with ab initio and DFT computations have been used to assign the vibrations of the molecule in its S0 electronic ground state and to calculate its structure. The ultraviolet absorption spectrum showed the electronic transition to the S1(π,π*) state to be at 37,820.2 cm(-1). With the aid of ab initio computations the vibrational frequencies for this excited state were also determined. TD-B3LYP and CASSCF computations for the excited states were carried out to calculate the structures for the S1(π,π*) and S2(n,π*) excited states. The CASSCF results predict that the S1(π,π*) state is planar and that the S2(n,π*) state has a barrier to planarity of 256 cm(-1). The TD-B3LYP computations predict a barrier of 124 cm(-1) for the S1(π,π*) state, but the experimental results support the planar structure. Hypothetical models for the ring-puckering potential energy function were calculated for both electronic excited states to show the predicted quantum states. The changes in the vibrational frequencies in the two excited states reflect the weaker π bonding within the pyridine ring.
采用红外和拉曼光谱以及从头算和密度泛函理论计算，对 2,6-二氟吡啶（26DFPy）的振动进行了归属，并计算了其结构。紫外吸收光谱显示，分子的电子跃迁到 S1(π,π*)态的能量为 37820.2cm(-1)。借助从头算计算，也确定了该激发态的振动频率。对激发态进行 TD-B3LYP 和 CASSCF 计算，以计算 S1(π,π*)和 S2(n,π*)激发态的结构。CASSCF 结果预测 S1(π,π*)态是平面的，而 S2(n,π*)态的平面性存在 256cm(-1)的势垒。TD-B3LYP 计算预测 S1(π,π*)态的势垒为 124cm(-1)，但实验结果支持平面结构。计算了两个电子激发态的环扭转势能函数的假设模型，以显示预测的量子态。两个激发态中振动频率的变化反映了吡啶环中较弱的π键合。
